The zoo's general manager, Mary Rayner, said zoo officials were worried for the koala's health because "it's his first winter" in New South Wales and at 13, he's considered elderly by koala standards.

The zoo acquired the koala early this year from a zoo in the warmer Gold Coast, and Rayner told the Telegraph that he had lost some weight during the move, so keepers were supplementing his diet of eucalyptus leaves with a special paste.

"We were hoping to get Banjo's weight back up before winter," she said.

"He was in his own enclosure because we were concerned about him and we wanted him to get used to his new home before we introduced him to any females."

Police are investigating the theft.

"We're all scratching our heads. To the best of our knowledge it's the first time a koala has been stolen from a zoo in Australia," Rayner said.

Two female koalas were stolen from the San Francisco Zoo in Dec. 2000. The animals were recovered within a day and two juvenile boys were arrested for the theft, according to the San Francisco Chronicle.